What does it mean, exactly, to claim a film as your "favourite"? Looking back over the choices made so far, it's clear that this is, firstly, a judgment that's felt, not thought; secondly, that it is precisely that: a claim, an act of appropriation. We feel a keen sense of ownership about the films we love the best – and when I first saw Together on a hungover Sunday cinema trip back in 2001, I came away feeling as if it had been written for me.

The film – which picks its way through a month or thereabouts in the life of a Swedish commune in 1975, from the announcement of Franco's death on November 20 to snowfall on Christmas morning – played out to me like a technicolour version of my own childhood: same concerns, similar conversations; but the knitwear a little bolder, the flares a fraction wider, the socialism (fewer jumble sales for striking miners, more ideological nudity over the breakfast table) that touch more picturesque. The central drama of a pair of siblings caught in the spindrift of their parents' separation chimed with me, too (as it doubtless did with 50% of the Sunday night audience). The elder of the two, specky, solemn Eva, was, in particular, all too easy to empathise with.

Together 2

The story, what there is of it, is small-scale, unexceptional. When her husband, Rolf, gets drunk and hits her, Elisabeth takes her children (13-year-old Eva and Stefan, six) to live with her brother Goran in Tillsammans, the commune he's established with a group of more-or-less like-minded souls in a Stockholm suburb. There's Lena, Goran's lover, who's rather keener on the idea of an open relationship than he is; newly lesbian Anna, her ex-husband Lasse, and their small son Tet (piously named for the Tet offensive); Klas, gay, who has his eye on Lasse; wild-eyed revolutionary Erik; and nuclear family Signe, Sigvard and Moon, who regard their fellow communists' lack of rigor with increasingly pursed lips. Life on the commune, when Elisabeth and the children arrive there, appears to be trundling along on an endless loop of chickpeas and porridge, wine and world-righting conversation, and rows about the washing up.

All of which risks making the set-up sound sitcom-ish, the characters, with their lumpy jumpers and alarmingly unflattering haircuts, like paper-thin caricatures. Not a bit of it. Together's surprising and glorious strength lies in the way in which it takes a potentially cartoonish situation, complicates it, and then complicates it further, stripping away our preconceptions both of these sorts of people and this sort of film to reveal the messy, mixed-up reality beneath. Circumstances which seem to be clear cut rapidly acquire gradations: over the course of two hours, we find ourselves feeling choking sympathy for a man who hits his wife and surreptitiously swigs vodka from a hipflask when dining out with his children, and outraged frustration towards a group of well-intentioned people who view themselves as working towards an egalitarian utopia but who flagrantly neglect the emotional lives of the children in their midst.

Together, directed by Lukas Moodyson

Those children, incidentally, are one of the film's great and understated virtues. Unlike your average Hollywood movie in which the children are deployed as foils for grown-up action, or, cynically, as devices to tug at our heartstrings, the children here are fully realised individuals who end up pretty much acting in a film of their own, their concerns only lightly aligned with the adults'. When Eva, caught on the agonising crux between childhood and maturity, has to climb out of the commune's beat-up campervan under the derisive stares of her classmates, her shame is made more unbearable by the fact that her kindly uncle thinks he's doing her a favour by driving her right up to the school gates. While the grown-ups are earnestly debating the difference between surplus value and profit, meanwhile, Stefan and Tet are playing "torture" and arguing over who gets to be Pinochet. The gulf between the generations is so wide here as to become the film's richest source of laughter.

Which is good, because laughter otherwise is thin on the ground. In the UK, Together has been marketed – inexplicably to my mind – as a sort of quaint, feel-good comedy; a sweet little film about sweet little foreigners, all dancing around to Abba. "Cinematic sunshine to warm the soul" bleats the quote from the Mail on Sunday on the front of the DVD. "A wonderful film! One of the most heartening films of the year!" trills Time Out, on the back. Well, it is wonderful. It is, in a sense, heartening. And there is indeed some Abba (of which more in a moment). But there's very little sunshine here, and the exclamation marks are teeth-grindingly supernumerary. Because for all the sense of claustrophobic proximity that life in the commune engenders, the title of the film is deeply ironic. This is, at heart, a film about loneliness; about our fumbling attempts to make connections and the ways in which, for all our best intentions, we fail. "There's strength in being alone – that's just bullshit," says Birger, Rolf's neighbour, and a man so awfully, profoundly lonely that he loosens the washer that Rolf has tightened on his sink so that Rolf will have to come round and fix it again. "Only thing worth anything is being together." He's right, and don't the characters know it – but the knowledge doesn't benefit them any. It just makes their failures more painful.

Lukas Moodysson's film Together

This isn't a light and frothy film: it offers neither its characters nor us any sops, any easy answers. The final scene of football in the snow on Christmas morning has the look of a happy ending, but is in fact as complicated and precarious as the fabled Christmas Day football match in the trenches: a momentary rapprochement that is beautiful and heartfelt but solves precisely nothing. The characters' ebullience, their delight in the game and each other, is made unbearably poignant by the knowledge that all the problems they're playing to forget will be right there waiting for them when they put the ball down again.

But just as Together isn't a straightforward comedy, it's not straightforwardly bleak, either. Like life, it leaves all options open. What saves the ending – and us – from spiralling into despair is the understanding that although there are problems lurking beneath the snow, beneath the problems is a bedrock of love. Love in Together is raw and rusty, at times unreciprocated, often inconvenient. But it is the engine of the film, endlessly sought and easily given, driving the actions of each of the characters. And it's the abundance of love – sexual, parental, filial, familial – that makes this a heartening film, that fills it with awkward, hopeful beauty.

The film opens, give or take a scene or two, on Elisabeth's wrenching departure from the family home: everyone in tears, Rolf storming and begging, and Abba's minor-key masterpiece SOS providing the soundtrack. In the final scene, when everything looks so superficially rosy, the song swells back in again, modulated and modified by all that's gone before. And it's the irreducible complexity of what we feel when we hear that piece of pop music for the second time that makes Together my favourite film. Rather than a melody, it has become a chord: joyful and painful at once, it offers you hope and at the same time shows you the hopelessness of it; it breaks your heart and leaves you smiling. The first time I heard it in that Sunday cinema, I felt like it had been written for me.